1. Field of the Invention
The present invention relates to flow meters for measuring the flow of fluid through a conduit. The flow meters described are particularly adapted for measuring the volumetric flow rate for a high pressure direct injection automotive fuel injection system. Also described is a software method of determining the volumetric flow rate for a periodic oscillating flow in a pipe from measurement of the instantaneous center line velocity.
2. Description of the Related Art
In automotive fuel injection systems, the power delivered by the engine is related to the shape of the spray, as well as the quantity and timing of fuel delivered to the combustion chamber. The design of fuel injectors and control of the operation of fuel injectors after installation would be greatly aided by a flow meter capable of providing data on the instantaneous volumetric flow rate in a fuel injection system, as well as a volumetric flow rate integrated over a specified time period, or a combination of the two. The present invention provides a flow meter which uses laser Doppler anemometry to measure the instantaneous center line velocity of fuel in a fuel pipe upstream from a fuel injector, and processes the data by Fourier transform using a novel exact solution to Navier-Stokes equations for any periodically oscillating flow to obtain the instantaneous volumetric flow rate of fuel in the system, as well as other desired flow characteristics.
Various devices for measuring fluid flow characteristics have been described previously. U.S. Pat. No. 3,548,655, issued Dec. 22, 1970 to M. J. Rudd, describes a laser Doppler velocimeter for measuring the velocity of fluid flow which measures the sinusoidal variation in light intensity as a particle in the fluid passes through interference fringes produced by laser beam which passes through a two slit mask. No means for measuring instantaneous velocity is described, nor is velocity necessarily measured on a center line. Further, no processing means for computing volumetric flow rate is described, and no means for indicating the direction of the velocity is described.
U.S. Pat. No. 3,825,346, issued Jul. 23, 1974 to J. Rizzo, reaches an interferometer for measuring fluid flow which uses two beams, a reference beam and a test beam, which travel equal path lengths and recombine to form an interference pattern. U.S. Pat. No. 3,937,087, issued Feb. 10, 1976 to W. S. Heggie, teaches a transducer for measuring pressure changes during fuel injection. The transducer is a resistive element in the form of a coil wrapped around the fuel line which varies in resistance as the fuel line expands and contracts, the difference in current through the coil being measured through a bridge.
U.S. Pat. No. 4,073,186, issued Feb. 14, 1978 to C. L. Erwin, Jr., describes a flow meter having a magnet mechanically attached to a valve, the magnet generating current in a magnetic pickup as the valve opens and closes for counting the flow pulses, the device releasing metered amounts of fuel with each pulse. The device appears to be for measuring fuel consumption, and not for regulating fuel flow into an injector. U.S. Pat. No. 4,192,179, issued Mar. 11, 1980 to E. Yelke, discloses a collar which fits around a fuel line to a fuel injector and has piezoelectric material affixed to the inside surface of the collar to develop an electrical signal as the fuel line expands and contracts.
U.S. Pat. No. 5,031,460, issued Jul. 16, 1991 to Kanenobu et al., teaches a device for detecting pressure changes in pipes. The device is a transducer with a bimorph piezoelectric transducer strapped around the pipe to sense expansion of the pipe as fluid is pulsed through the pipe. European Patent No. 489, 474, published Jun. 10, 1992, describes a laser apparatus for measuring the velocity of a fluid which uses an interferometer type device with a laser beam split into a reference beam and a measurement beam which is reflected back through the fluid so that the back scatter is compared to the reference beam to measure velocity. No method for processing the velocity to compute volumetric flow rate is described.
Japanese Patent No. 8-121,288, published May 14, 1996, shows a device for measuring injection rate with a pressure sensor for measuring the force of injection and a laser Doppler anemometer for measuring velocity, and which uses a mathematical formula which relates force and velocity to flow rate. Japanese Patent No. 8-121,289, published May 14, 1996, describes a device which uses two laser Doppler anemometers, one in the main supply line, the other in a bias flow generating unit fed by a divider pipe, to measure the flow rate by a differential flow rate method.
Applicant has co-authored several publications which disclose flow measuring devices. An article titled “Measurement of instantaneous flow rates in periodically operating injection systems” by F. Durst, M. Ismailov, and D. Trimis, published in Experiments in Fluids, Vol. 20, pp. 178-188 in 1996, describes a technique for measuring instantaneous flow rates using laser Doppler anemometry to measure center line velocity in a capillary pipe and an improved solution of the Navier-Stokes equations for any periodically oscillating flow to calculate instantaneous volumetric flow rate. The device measured the flow of water released by a magnetically operated valve through a 2 mm diameter tube.
A paper presented at the Flomeko '98 9th International Conference on Flow Measurement in June, 1998, titled “Accurate LDA Measurements of Instantaneous and Integrated Flow Rates in High Pressure Gasoline Injection System” by Ismailov et al., describes a device for measuring flow rate in a gasoline injection system at 7 MPa with a Unisia Jecs swirl injector. The device uses a 16 mW He—Ne laser directed through a beam splitter and frequency shifted by Bragg cells, focused by a lens to form a measurement control volume 485 μm in length and 46 μm in diameter on the center line of a quartz pipe 300 mm long having an inner diameter of 3.5 mm. The light is scattered by heptane and detected through a pinhole by a photomultiplier tube elevated at a 30°, the output being processed by a DOSTEK interface board. The center line velocities are processed according to the method set forth in Durst, supra.
A paper presented at the 3rd ASME/JSME Joint Fluids Engineering Conference Jul. 18-23, 1999 titled “Instantaneous Flow Rates in Gasoline Direct Injection System By Means of LDA and Bosch Meters” by Ismailov et al., and an article titled “LDA/PDA measurements of instantaneous characteristics in high pressure fuel injection and swirl spray” by Ismailov et al. in Experiments in Fluids, Vol. 27, pp. 1-11 (1999) present similar studies and describe similar measuring devices to those presented in the Flomeko article, supra.
None of the above inventions, patents, and publications, taken either singularly or in combination, is seen to describe the instant invention as claimed. Thus a flow meter solving the aforementioned problems is desired.